Ellen DeGeneres’s celeb-studded selfie from the most-watched Oscars telecast in a decade was a landmark social media moment at a time online conversation is boosting television viewership and vice versa.

It’s also a murky example of what is or isn’t product placement in a hyper-marketed world. Would the world’s most retweeted photo have been shot by an iPhone if Samsung hadn’t been a commercial sponsor of the Academy Awards?

An estimated 43 million people watched ‘‘12 Years a Slave’’ win the Oscar for best picture on Sunday night. It was the most-watched Academy Awards since 2004, when ‘‘Lord of the Rings: Return of the King’’ was the best picture. And it was the most popular entertainment event on TV since the ‘‘Friends’’ finale that year. The Oscars are generally the most-watched TV event of the year after the Super Bowl.

Oscar night was also big for Jimmy Kimmel. The ABC late-night star drew just under 7 million viewers for his post-Oscars special, the biggest audience he’s ever gotten on ABC, despite starting at 12:42 a.m. on the East Coast.

The ratings provide further evidence of how big event programming is a growth engine for broadcast networks, in large part because of fans watching the event and conversing with friends on tablets and smartphones. Twitter said that some 14.7 million tweets mentioning the Oscars or prominent actors and films were sent out during the Sunday night telecast, and Facebook said there were 25.4 million interactions about the show.

No social media moment was bigger than when host DeGeneres briefly caused Twitter to crash after going into the audience and asking Bradley Cooper to take a picture with several other stars crowding around. Besides Cooper and DeGeneres, Meryl Streep, Jennifer Lawrence, Kevin Spacey, Julia Roberts, Angelina Jolie, and Brad Pitt also crowded into the frame. She asked viewers to help her set a retweet record, and they quickly complied.

By Monday afternoon, it had been retweeted some 2.8 million times, shattering the previous record of 810,000 retweets for the photo of President Obama and first lady Michelle Obama hugging after the 2012 election. Twitter was humming at 254,644 tweets per minute after DeGeneres’s request, and the company said the crush disrupted service for 20 minutes.

DeGeneres handed a Samsung device to Cooper to take the selfie. Since the Oscars host’s Twitter posts from backstage included shots from an iPhone, Samsung doesn’t seem to be her usual smartphone of choice.

Samsung, however, was a big presence at the Oscars besides being a commercial sponsor. The company gave its phones to student presenters and encouraged them to tweet and post on Instagram with them. Dozens of Samsung phones, tablets, and TVs were used to make a digital photo display in the backstage green room.

ABC said Samsung did not pay specifically for use of the camera in DeGeneres’s selfie segment and the company wasn’t explicitly named on the air as the stunt unfolded, but it is a noticeably larger device than an iPhone. Spokeswoman Nicole Marostica said once producers decided to do the segment, it made more sense to use a Samsung product because the company was an Oscars sponsor.

‘‘They were just lucky beneficiaries of the whole thing,’’ Marostica said.

Use of the Samsung phone ‘‘is a wonderful example of product placement,’’ in part because it seemed so natural, said Tim Calkins, marketing professor at the Kellogg School of Business at Northwestern University.